Systems and methods for self-calibration

ABSTRACT

A self-calibrating integrated circuit includes a processor having at least one analog function used with the processor; one or more sensors adapted to sense one or more environmental parameters of the at least one analog function; and a solid state memory being configured to store the one or more environmental parameters of the at least one analog function.

This application is a continuation of U.S. patent application Ser. No.11/011,990, now U.S. Pat. No. 7,023,286, filed Dec. 14, 2004 entitled“SYSTEMS AND METHODS FOR SELF-CALIBRATION,” which is a continuation ofU.S. patent application Ser. No. 09/930,828, now U.S. Pat. No.6,850,125, filed Aug. 15, 2001, the contents of which are herebyincorporated by reference.

BACKGROUND

The present invention relates systems and methods for self-calibratingsemiconductor devices.

Today's modern electronic products such as computers and high definitiontelevisions rely on advanced integrated circuits (ICs) that operate athigh speed. These products in turn rely on a clock source and clocksignal that act as a master timing element for control of hardware.

Traditionally, a master clock source is generated off-chip and providedas an input to the ICs. One method for generating the clock signal usescrystals. While this method is well known and is reliable, off-chipgenerators take valuable circuit board space and have minimum heightrestrictions. A crystal-based system also requires extra pins forconnecting the crystal to an integrated circuit requiring the clocksignal. The crystal generator also requires external resistors andcapacitors, adding cost, but more importantly takes more board space.Other disadvantages include an inability to operate over extendedvoltage ranges; long start times when power to the system is turned on;and high power consumption, making the systems less attractive inbattery-powered applications.

On-chip oscillators have been designed for applications that demand lowcost and low power consumption and applications that can't afford thespace or pin requirement that crystal oscillators demand. For instance,ring oscillators have been used in IC designs where an exact clocksignal is not required. Large performance variations, however, may beseen by the system as the ring oscillator frequency can vary overprocess differences, voltage variations and temperature excursions.

Yet another solution that designers have devised is to use ofresistor-capacitor (RC) oscillator designs. RC oscillators lack thefrequency accuracy of crystal oscillators, but are advantageous in thatthey can allow instant start-up of the clock signal from a stoppedstate. They also have low power consumption. However, when using analogelectronic components such as those in the RC oscillator, it may bedifficult to obtain precise voltages or measurements because analogcomponents have many parameters that vary with process, temperature orpower supply. For example, one or more reference voltages for anintegrated circuit may be generated from a bandgap reference voltagecircuit. If, however, the bandgap reference voltage is not accurate dueto variations in power supply or temperature, then all referencevoltages derived therefrom will also be inaccurate. This could inducesubstantial errors in the operation of the integrated circuit.

SUMMARY

In one aspect, a self-calibrating integrated circuit includes aprocessor having at least one analog function used with the processor;one or more sensors adapted to sense one or more environmentalparameters of the at least one analog function; and a solid state memorybeing configured to store the one or more environmental parameters ofthe at least one analog function.

Implementations of the above aspect may include one or more of thefollowing. One analog function can be provided by an oscillator. The oneor more environmental parameters includes temperature or supply voltage.The one or more sensors include one or more temperature sensors, whichcan be diodes with metallization to screen out light. The one or moresensors include one or more hot-electron sensors, which can include deepwell diodes. The one or more sensors include one or more hot electrongenerators such as ring oscillator-based hot electron generators. Theone or more sensors include one or more heaters, which can includepolysilicon resistors placed over a diode and transistors. The outputsof the sensors are provided to an analog switch. An analog to digitalconverter can be connected to the analog switch and to the processor toprovide environmental data.

This type of A/D converter is typically included in mixed-signal systemsalready, so only a MUX is necessary for the autocalibrator. The A/Dconverter can be used at very low frequencies (since environmentalfactors like temperature do not change very fast) and it can beimplemented with an inexpensive delta-sigma configuration.

Advantages of the invention may include one or more of the following.The system eliminates an external clock by using temperature compensatedRC generator. The embedded FLASH memory holds self-calibration data.Each chip self calibrates during testing. Basically, the on-board ringoscillator is compared to a highly accurate crystal oscillator outputduring testing. The temperature is then varied using the on-chippolysilicon heater or a hot/cold chuck on the test system. Also, thevoltage supply is varied to evaluate the impact of voltage on clockoutput. Additionally, the chip has temperature sensors at key locationsacross the chip. These sensors can be sensed using an on-chip A/Dconverter. The system minimizes wide variations in clock signalfrequency over operating parameter variables such as voltage andtemperature. The resulting ring oscillator is accurate for flash memoryoperation, requires less power, fewer pins and has fast start-stopgating. The system optimizes operating performance by dynamicallymonitoring environmental parameters and adjusting the operation andclock signal frequency. The system reduces cost by eliminating anexternal crystal clock. The system also frees up one or more pins thatare normally dedicated to clock input signals. External precisioncomponents are not necessary since the FLASH memory calibrates thechip's mixed signal circuits to generate a precise, repeatable clocksignal. The system maintains accurate clock signals over extended periodsince it has extensive self-test modes that allow it to self-calibrate.

The system achieves a low cost but sophisticated product which may beused in critical and precision applications that require calibrationafter manufacture of the individual functions of the system, andheretofore could only be implemented with more costly andspace-consuming externally adjustable discrete components.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 shows an exemplary IC with self-calibration capability.

FIG. 2 shows an exemplary process for maintaining an oscillatingfrequency.

DESCRIPTION

FIG. 1 shows an exemplary IC 10 with a digital portion 20 and an analogportion 40. The digital portion 20 includes a processor 12 and memoryarray 14, among others. The memory array 14 can be static random accessmemory (SRAM), dynamic random access memory (DRAM), and a FLASH memory,among others. The analog portion 40 also includes an on-chip clockoscillator 42 and one or more analog circuits 44 such as radio frequency(RF) transceivers or optical transceivers, for example.

The on-chip clock oscillator 42 can be a ring-oscillator or an RCoscillator or an LC oscillator. Typically, as known in the art, a ringoscillator includes a series of discrete components includingtransistors, capacitors, among others. For example, as discussed in U.S.Pat. No. 6,211,744 to Shin and U.S. Pat. No. 6,154,099 to Suzuki, etal., a conventional ring oscillator can be formed by connecting an oddnumber of inverters in a ring shape. In such a configuration, if Y isthe state (signal level) at a connection point, the Y signal is invertedto Y by the next-stage inverter, and the Y is further inverted to Y bythe second next-stage inverter. The signal level is sequentiallyinverted, and becomes Y at the connection point through one roundbecause an odd number of inverters are connected. Through one moreround, the signal level becomes the original Y. In this manner, the ringoscillator self-oscillates. An oscillation output is obtained from theoutput node of an arbitrary inverter.

Another conventional ring oscillator can use a NAND gate circuit forcontrolling start/stop of oscillation is inserted in a ring formed byconnecting a plurality of even number of inverters. The start/stop ofoscillation is controlled by externally inputting an “H”- or “L”-levelcontrol signal CNT to the NAND gate circuit. That is, the control signalCNT is first set at “L” level and then changed to “H” level to startoscillation. When the control signal CNT is at “L” level, an outputsignal from the NAND gate circuit is fixed at “H” level. Outputs fromthe odd-numbered inverters change to “L” level, outputs from theeven-numbered inverters change to “H” level, and the initial states ofthe output levels of the respective inverters are determined. In thisstate, the ring oscillator does not oscillate. When the control signalCNT changes to “H” level, the NAND gate circuit substantially operatesas an inverter, and the ring oscillator oscillates in the above mannerwhere an odd number of inverters are connected in a ring shape.

The frequency of the oscillation signal from the conventional ringoscillator depends on the number of stages of inverters and a wiringdelay. Hence, the lower oscillation frequency is obtained by increasingthe number of stages of inverters and the length of the signal line.This increases the circuit size. Further, although thevoltage-controlled oscillators have an identical circuit configuration,they have different oscillation frequencies due to certain factors ofthe production process. For example, the process can affect the gatedelay time that can affect the precision of the oscillator.

The RC oscillator allows quicker oscillation time. A number ofconventional RC oscillators can be used. For example, as discussed inU.S. Pat. No. 5,739,728, an RC oscillator has a capacitor C1, first andsecond resistors R1 and R2, a comparator COMP and a switch S1. When thevoltage across the capacitor C1 is less than a bias voltage, the outputof the comparator is at a logic low level and switch S1 is open. Thecapacitor is charged by current flowing through resistor R1 from avoltage source. When the voltage across the capacitor exceeds biasvoltage, the output of the comparator switches to a high logic levelwhich closes switch S1. The capacitor is then discharged throughresistor R2. When the capacitor voltage drops back below the biasvoltage, the comparator opens switch S1, thereby beginning a new cycle.As with the ring oscillator, the RC oscillator also faces frequencydrift caused by process, temperature and voltage variations.

To capture information that allows the processor 12 to automaticallycalibrate the IC 10 so that the on-chip clock oscillator 42 is preciseand accurate in spite of process, temperature or power supplyvariations, various sensors 46–48 are placed at predetermined locationsin the IC 10 to sense environmental variations.

The analog portion 40 includes one or more temperature sensors 46, whichcan be diodes with metallization to screen out light. The output fromthe temperature sensors 46 are eventually digitized and provided to theprocessor 12 for adjusting the IC 10. To calibrate the temperaturesensors 46, the analog portion 40 also has one or more heaters 52, whichcan be polysilicon resistors placed over a diode and transistors. Theheaters 52 can also be used to bring the IC 10 to a predeterminedtemperature range if the IC 10 is below its normal operatingtemperature.

The analog portion 40 also includes one or more hot-electron sensors 48,which can be deep well diodes. The term hot-electron effect refers tothe phenomenon of electrons which originate from FET surface channelcurrents, from impact ionization currents at the FET drain junction, orfrom substrate leakage currents. Electrons drifting from the gate maygain sufficient energy to enter into the gate, or they may collide withthe silicon atoms and generate electron-hole pairs. The hole adds tosubstrate current, and the secondary electron may be injected into thegate of a subsequent FET. The deep well diodes sense the hot electroneffect and provide this information eventually to the processor 12 toautomatically compensate for hot electron effects. To providecalibration data for hot electron characterization of the IC 10, theanalog portion 40 also includes one or more hot electron generators 50such as small ring oscillators.

The outputs of the sensors 46–48 are provided to analog switch 53 thatin turn is connected to a precision analog to digital converter 54(ADC). The analog switch 53 is controlled by the processor 12 to selectthe output of one of the sensors 46–52 to the input of the ADC 54 todigitize autocalibration data. In one implementation, the ADC is a 12bit ADC. The output of the ADC 54 is provided to the processor 12 tomake decisions and the flash memory in the memory array 14 to store theautocalibration data.

The processor 12 can check the temperature at different locations on theIC 10 and average the temperature being sensed to better adjust to theactual temperature present. By monitoring the temperature of the IC 10,the processor 12 can detect whether the oscillator 42 is deviating fromits specified frequency. In one embodiment, the flash memory has aparameter array with one element storing the operating temperature ofthe IC 10. The operating temperature information is used to generatediffering delays based on circuit characteristics and based ontemperature-induced shifts in oscillator frequency. The processor 12adjusts the timing when the temperature changes outside the nominalsetting by changing the number of the delay stages to compensate for thetemperature range variations.

In addition to the temperature adjustments made by the controller, thesystem can also detect the supply voltage that the system is presentlyoperating at and adjust for variations in the supply voltage. Like thetemperature, the voltage represents an offset from the nominal voltagesetting. If the operating voltage is not at a nominal value, thecontroller adjusts the ring oscillator delay path to compensate for thevoltage differential. Environmental parameters of the IC 10 includetemperature, supply voltage and other external parameters which effectthe performance of the IC 10. Additional details on the device thatcorrects temperature and voltage variations are discussed in aco-pending patent application entitled “Ring Oscillator DynamicAdjustments for Auto-calibration” and having Ser. No. 09/930,822, andnow U.S. Pat. No. 6,853,259, filed Aug. 15, 2001, the content of whichis hereby incorporated by reference.

An exemplary process of calibrating and correcting the IC 10 is shown inthe flow chart 200 of FIG. 2. First, the IC 10 is initialized (step201). The process 200 checks for user adjustments (step 202). If a userwants to adjust the operating frequency of the clock to meet thetemperature and voltage conditions of the application, the process 200adds the adjustments so that the oscillator moves toward the userspecified operating frequency.

Next, in step 203, voltage, hot electron and temperature calibrationsignals are sent to the voltage generators, hot electron sources andheaters, respectively. These calibration signals are preferablygenerated by the processor 12 of FIG. 1 so that they have a known leveland can be swept over a known test range. In process step 204, the hotelectron sensor responses are monitored. In decision step 206, the hotelectron sensor responses are averaged and the averaged result iscompared to a predetermined range. If the response is out of range, itis corrected in process step 208. The above steps are performed for eachsensor type. For example, in step 210, the temperature sensors aremonitored. In decision step 216, the temperature responses are averagedand the averaged result is compared to a predetermined range. If theresponse is out of range, it is corrected in process step 218. Next, instep 220, the voltage sensors are monitored. In decision step 226, thevoltage responses are averaged and the averaged result is compared to apredetermined range. If the response is out of range, it is corrected inprocess step 228. In the above manner, each sensor type is monitored andthe environment sensed by the sensor type is adjusted. For example, ifthe temperature gets hotter (indicating slower silicon and slower ringoscillator) the flash system will move the oscillator settings to thefaster settings to compensate for the slow down because of increasedtemperature or a corresponding decrease in operating voltage.

The data is continually collected. This is done by having the processor12 instruct the switch 53 to connect to each sensor 46–52 in seriatimand the ADC 54 to digitize the environmental parameters, and the FLASHmemory file to store the output of the ADC 54 (step 240). The FLASHmemory file can store one sample point for each sensor, or can storehistorical data for the sensors.

To keep a constant clock frequency, the process 200 moves the oscillatoras to the environmental changes. Moreover, the processor 12 can predictthe environmental changes based on historical data.

Additionally, the process can calibrate sub-systems. For example, withrespect to the wireless transceiver, responses that can be calibratedand corrected in with calibration signals from the processor 12 caninclude transmit/receive gain over temperature, transmit/receive gainover voltage, transmit/receive gain over hot electron effect, andfrequency responses of the PLL's voltage-controlled oscillator andfrequency steps of a phased-lock loop as function of voltage,temperature and hot electron level, for example. This process ofcalibration and correction can be conducted for each sub-system of theIC 10.

The term “FLASH memory” is used above to generally describe anynon-volatile technology. The present invention applies to allnon-volatile floating gate technologies such as EEPROM and FLASH memory.Additionally, RAM storage where the contents of the RAM are maintainedfor an extended period (more than 1 year) by an external battery sourcewould also be within the scope contemplated by the present invention aswell as any method of memory that is erasable and electricallyprogrammable.

Moreover, although a self-calibrated clock has been discussed above,other self-calibrated functions are contemplated and within the scope ofthe invention. These functions include: analog-to-digital converter,digital-to-analog converter, voltage reference, current reference,timer, amplifier having a calibrated frequency response (high or lowpass filter), offset voltage adjustment, bandpass filter (frequencydetection), television or radio tuner, temperature transducer amplifier(linear and non-linear temperature profiles), pressure transduceramplifier, analog multiplier and divider, among others.

Although specific embodiments of the present invention have beenillustrated in the accompanying drawings and described in the foregoingdetailed description, it will be understood that the invention is notlimited to the particular embodiments described herein, but is capableof numerous rearrangements, modifications, and substitutions withoutdeparting from the scope of the invention. The following claims areintended to encompass all such modifications.

1. An integrated circuit, comprising: a digital portion including aprocessor; an analog portion including a radio frequency circuitconfigured to communicate radio frequency data; a plurality of sensorsconfigured to sense environmental parameters; a memory configured tostore self-calibration data; and wherein the processor is configured toadjust a portion of the integrated circuit based on the sensedenvironmental parameters.
 2. The integrated circuit of claim 1, furthercomprising a multiplexer configured to provide an output of theplurality of sensors to the processor.
 3. The integrated circuit ofclaim 2, further comprising an analog-to-digital converter coupledbetween the multiplexer and the processor.
 4. The integrated circuit ofclaim 3, further comprising an oscillator coupled to the radio frequencycircuit.
 5. The integrated circuit of claim 4, wherein the processor isconfigured to adjust the oscillator based on the sensed environmentalparameters.
 6. The integrated circuit of claim 1, wherein theenvironmental parameters include at least one of temperature and supplyvoltage.
 7. The integrated circuit of claim 1, wherein the plurality ofsensors includes one or more hot-electron sensors.
 8. The integratedcircuit of claim 1, further comprising one or more hot-electrongenerators.
 9. A method comprising: sensing at least one environmentalparameter associated with a semiconductor device via at least one sensoron the semiconductor device, wherein the semiconductor device includesan analog portion including a radio frequency circuit configured tocommunicate radio frequency data and a digital portion; and controllinga clock frequency of the semiconductor device based on the sensed atleast one environmental parameter.
 10. The method of claim 9, furthercomprising comparing the sensed at least one environmental parameter toa predetermined value for the at least one environmental parameterstored in a memory.
 11. The method of claim 9, further comprisingadjusting the clock frequency using an oscillator of the semiconductordevice.
 12. The method of claim 9, wherein sensing the at least oneenvironmental parameter comprises sensing a hot-electron effect of thesemiconductor device.
 13. The method of claim 9, further comprisingadjusting a temperature of the semiconductor device if a sensedtemperature is below a predetermined value.
 14. The method of claim 13,further comprising adjusting the temperature via one or more heaters ofthe semiconductor device.
 15. A system comprising: a processor; a radiofrequency circuit coupled to the processor; an oscillator coupled to theprocessor and the radio frequency circuit, the oscillator having afrequency controllable by the processor based on analysis of one or moreenvironmental parameters; and a plurality of sensors configured to sensethe one or more environmental parameters, wherein at least one of thesensors comprises a hot-electron sensor.
 16. The system of claim 15,further comprising a memory configured to store information regardingthe one or more environmental parameters.
 17. The system of claim 15,wherein the processor is configured to send calibration signals tosources of the one or more environmental parameters.
 18. The system ofclaim 17, wherein the processor is configured to average outputs of asubset of the plurality of sensors.
 19. The system of claim 16, whereinthe memory is configured to store self-calibration data for theoscillator, the self-calibration data obtained during testing.
 20. Thesystem of claim 15, wherein the processor is configured to predictchanges to the one or more environmental parameters based on historicaldata.